Identify this type of aluminum?

[GunsOfNavarone]

Hey guys & girls, I am replicating some parts and the current ones, I’m quite sure, are a TYPE of aluminum….but no idea what.
I would normally say cast, as they are very crystallized inside, but theses are oxidizing badly to where they peel. Also, if the were cast, they would be machined as they are very precision, but these most obviously are not machined (at least not on the external surfaces. I have read about a lot of odd aluminum types, but that’s not really help g me here. Ideas?
Another point, they are light like 6061, but much harder. You couldn’t run a nail along these and scratch them.

 

[ChazzC]

Hey guys & girls, I am replicating some parts and the current ones, I’m quite sure, are a TYPE of aluminum….but no idea what.
I would normally say cast, as they are very crystallized inside, but theses are oxidizing badly to where they peel. Also, if the were cast, they would be machined as they are very precision, but these most obviously are not machined (at least not on the external surfaces. I have read about a lot of odd aluminum types, but that’s not really help g me here. Ideas?
Another point, they are light like 6061, but much harder. You couldn’t run a nail along these and scratch them.

Diecast parts, which this looks like, are usually smooth (think of diecast zinc items). The surface hardness could be from anodizing.

 

[GunsOfNavarone]

I definitely lean towards due cast aluminum, I guess I didn’t think about anodizing. I wouldn’t think that anodized layer would peel like this, but I don’t have a better explanation.

 

[ChazzC]

Anodizing basically opens pores in the surface so it can be dyed and then a surface coating is applied. Any coating can fail, particularly if there’s poor preparation.

 

[verbotenwhisky]

I definitely lean towards due cast aluminum, I guess I didn’t think about anodizing. I wouldn’t think that anodized layer would peel like this, but I don’t have a better explanation.

Or pewter would have similar characteristics.

 

[MrWhoopee]

Or pewter would have similar characteristics.

except heavier.

The color of the part looks like hard anodize.
The corrosion looks like aluminum when in contact with steel (or other dissimilar metal) and water or other conductive solution.

 

[Dabbler]

but theses are oxidizing badly to where they peel

Anodizing peels like this. Not coated, coated, whatever. The anodizing is a series of perforations very small, between .010 and .030 deep, depending on the process and intent. "hard anodizing" is nothing substancially different . Each of the tubes is coated in Aluminum oxide that is captive in the tubes. This improves the durability of the softer aluminum around it. it is these tubes that holds onto the dye to colour the metal. the dye is just normal fabric or food colouring.

But because of all these perforations, this is a way for moisture to get into the structure and corrode it from underneath. Once this process begins, it is all over.

If you want to reuse this aluminum, you have to sand/grind all this away before machining - that top layer is acutally quite weak, but is is a better wear surface (before oxidizing).

 

[wayback machine]

Peeling off like that, are you sure it isn't plated? I'm pretty sure they can even chrome plate aluminum.
From my experience, anodizing just forms pits when it starts breaking down, not peeling like that.

 

[RJSakowski]

Anodizing basically opens pores in the surface so it can be dyed and then a surface coating is applied. Any coating can fail, particularly if there’s poor preparation.

Anodizing converts the surface of aluminum oxide. The nature of the crystal growth is such that the surface has small tubes perpendicular to the surface and the coating is porous and can accept dye. When the anodizing,by heating in boiling water, the pores close over trapping the dye and sealing the surface. No additional coating is necessary. Then anodizing is compromised, it just falls away. It wouldn't peel as shown above.

Plating, on the other hand will peel. It is common to plate Zamak parts for protection against corrosion and to enhance appearance. When the plating is compromised, corrosion can occur underneath the plating, causing it to peel as shown. Zamak is tupically harder than a aluminum and metals like nickle are often used for plating which can further enhance surface hardness.

 

[pontiac428]

ZAMAK is a form of pot metal that Atlas/Kalamazoo tried to pass off as an engineered material. It casts well, it's cheap, and it is surprisingly tough compared to typical white metals.

Sand it off and paint it, it should last a long time. If you don't want to paint it, polish it and use Johnson's wax. Seal it up.